The present invention relates to a toroidal continuously variable transmission for vehicles.
In a continuously variable transmission (hereafter, CVT), a pair of power rollers is gripped between an input disk and an output disk facing each other. The power rollers transmit a torque from the input disk to the output disk by friction. The power rollers are supported by trunnions.
When the trunnions are displaced in the direction of the trunnion axes, the contact positions of the power rollers and the disks change and the direction of the force exerted by the disks on the power rollers will vary. Due to this variation of force, the power rollers rotate together with the trunnions, and as a result, the contact radius of one of the input disk and the output disk increases, while the contact radius of the other disk decreases. The variation of these contact radii causes a variation of the ratio of the rotation speeds of the input disk and the output disk, i.e., a speed ratio. Thus, the speed ratio of the transmission can be made to vary continuously by displacing the trunnions in the trunnion axis direction. The rotation angle about the trunnion axis is referred to as the gyration angle of the power roller, and corresponds directly to the speed ratio of the CVT.
Here, when the power rollers are gripped between the input disk and the output disk, the input disk and the output disk respectively deform in an overturn direction. In order for the power rollers to follow the deformation in this overturn direction and maintain contact with both disks, they must follow the deformation of the disks in the overturn direction and must displace in the direction perpendicular to the trunnion axis and a power roller rotation axis.
To displace the power rollers in such a direction, the power rollers may be supported free to pivot on the trunnions via pivot shafts as disclosed in JP-A-H6-129509 published by the Japanese Patent Office in 1994. However, when a pivot shaft is used, the power rollers will displace not only in the above-mentioned direction but also in the direction perpendicular to it. Moreover, machining of the pivot shaft is difficult and the manufacturing cost of the pivot shaft is high. As it is necessary to provide a hole in the trunnion for supporting the pivot shaft, the strength of the trunnion decreases.
In this regard, in JP-A-H7-198014 published by the Japanese Patent Office in 1995, the pivot shaft is made unnecessary by supporting the power rollers free to slide in the direction perpendicular to the trunnion axis and the power roller rotation axis via a roller bearing unit comprising plural needle rollers and a cage which houses the plural needle rollers.
However, in the construction disclosed in JP-A-H7-198014, if the power rollers repeatedly slide due to the deformation of the input and output disks, the cage will slide due to the contact of the needle rollers and the cage. At this time, the magnitude of the force which acts on the cage when the power rollers are pushed and the cage slides, is different from that of the force which acts on the cage when the force acting on the power rollers is released and the cage returns, so the cage does not return to its original position completely.
Consequently, the cage protrudes from the trunnion, the needle rollers are gathered on one side, the force acting on the trunnion via the needle rollers is biased to one side, and the load acting on the power rollers can no longer be properly supported. Moreover, the protruding cage interferes with the input and output disks. This also occurs when the roller bearing unit is attached to the trunnion with an offset during assembly.
It is therefore an object of this invention to arrange that the cage of the roller bearing unit does not protrude from the trunnion, to prevent the situation that the load acting on the power rollers cannot be supported sufficiently, and to prevent the protruding cage from interfering with the input and output disks.
In order to achieve above object, this invention provides a toroidal continuously variable transmission comprising an input disk, an output disk facing the input disk, a power roller gripped between the input disk and the output disk, a pedestal which supports the power roller free to rotate about a power roller rotation axis, a trunnion which gyrates about a trunnion gyration axis, and a roller bearing unit which comprises a cage housing a roller and supports the pedestal on the trunnion so that the pedestal is free to slide in the direction perpendicular to the trunnion gyration axis and power roller rotation axis. A limiting member, which limits the slide amount of the cage of the roller bearing unit relative to the trunnion, is provided on the trunnion.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.